Evaluating Efficiency of UVC Air Sanitizing Devices and Systems

In choosing the best mobile or HVAC UV air sanitizing devices and systems it is important to be able to go beyond advertising claims, and have a quantitative evaluation method that produces a consistent metrics for a UV light air sanitizing system. With such a method supported by experiments, the consumers will be able to grade the systems with high degree of confidence.

An effective air sanitizing system must destroy viruses in the air rapidly after they are accidentally released into the indoor air by infected people. Therefore, our method focuses on the dynamics of the virus release and spread in the indoor air putting premium on the system’s ability to respond reliably and rapidly in disinfecting the aerosols produced from time to time by sneezing or coughing.

N5Air method in predicting the efficiency of a UVC air sanitizing system is based on two key factors: reliable destruction of viruses and rapid air processing. We consider both factors equally important, and thus the effectiveness of a system is calculated as a linear product of these two factors. While further experiments are needed to refine our calculation, we are confident that the N5Digital method correctly captures the two functions of an effective UVC light air sanitizing system.

1. UVC light air sanitizing devices must reliably destroy viruses, and

2. UVC light-based air systems must rapidly sanitize the indoor air by circulating it through the UVC light air

sanitizing devices.

The N5Air method predicts the air sanitizing system effectiveness, SSE as a product of two factors, relative power factor, RPF and the air recirculation factor, ARF:

SSE = RPF x ARF.

RELATIVE POWER FACTOR

The first multiplier, RPF in the metrics formula is defined as:

RPF = Peff/Vdev,

where

- Peff is the effective power of UVC source of the device. Peff is equal to the actual power of UVC source or lamps in expressed in kW multiplied by the UVC light reflectiveness factor. Our experiments showed that an appropriate reflector can effectively increase the power of the UVC source by several times.

- Vdev is the volume of the device’s chamber (m3) containing the UVC light.

AIR RECIRCULATION FACTOR

The air recirculation factor, ARF is the ratio of the air flow rate through the sanitizing device, W (m3/sec) and the total volume of the indoor air space being sanitized, Vspace (m3):

ARF = W/ Vspace.

Note that 1/ARF is the time in seconds required for circulating the air of the indoor space through the sanitizing device once. Larger values of ARF provide faster response of the air sanitizing system in dynamic situations.

We intend to identify reliable quantitative information on lethality of UVC light for different viruses present in the air (e.g., dependence of time needed to destroy the virus as a function of RPF). Until then, the N5Digital method will blends physics, biology, and ventilation into one number, relative SSE.

N5Air is using its method for evaluating and comparing various UVC systems presently available on the market.

Virus-free indoor air space